So, how should I approach the Firefox developers (or branding team)?
or should I merely rename the browser in Debian to something like
Icerabbit (you get the idea) to skirt these thorny legal issues. It
seems OpenOffice.org has similar restrictions on their logo
(http://www.openoffice.org/about_us/summary.html), how were they
handled?

The solution's obvious; name the Debian package and program within it
"phoenix".
$ apt-get install phoenix
$ phoenix

Well the reason the firefox developers renamed phoenix was because
that name had legal problems of it's own. And that doesn't solve the

problem of It's-called-Firefox-everywhere-except-Debian.

Fir---x ? :P
IMO, it's time to move it to -legal and contact the Mozilla developers.
Thanks,
Gustavo Franco